firewire: sbp2: add workarounds for 2nd and 3rd generation iPods

According to https://bugs.launchpad.net/bugs/294391
  - 3rd generation iPods need the "fix capacity" workaround after all
    (apparently they crash after the last sector was accessed),
  - 2nd generation iPods need the "128 kB maximum request size"
    workaround.

Alas both iPod generations feature the same model ID in the config ROM,
hence we can only define a shared quirks list entry for them.  Luckily
the fix capacity workaround did not show a negative effect in Jarod's
tests with 2nd gen. iPod.

A side note:  Apple computers in target mode (or at least an x86 Mac
mini) don't have firmware_version and model_id, hence none of the iPod
quirks list entries is active for them.

Tested-by: Jarod Wilson <jarod@redhat.com>
Acked-by: Jarod Wilson <jarod@redhat.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>